package blade.kit.io;

import java.io.Closeable;
import java.io.Flushable;
import java.io.IOException;
import java.io.Writer;
import static blade.kit.Assert.checkNotNull;

/**
 * Writer that places all output on an {@link Appendable} target. If the target
 * is {@link Flushable} or {@link Closeable}, flush()es and close()s will also
 * be delegated to the target.
 *
 * @author Alan Green
 * @author Sebastian Kanthak
 * @since 1.0
 */
class AppendableWriter extends Writer {
  private final Appendable target;
  private boolean closed;

  /**
   * Creates a new writer that appends everything it writes to {@code target}.
   *
   * @param target target to which to append output
   */
  AppendableWriter(Appendable target) {
    this.target = checkNotNull(target);
  }

  /*
   * Abstract methods from Writer
   */

  @Override public void write(char cbuf[], int off, int len)
      throws IOException {
    checkNotClosed();
    // It turns out that creating a new String is usually as fast, or faster
    // than wrapping cbuf in a light-weight CharSequence.
    target.append(new String(cbuf, off, len));
  }

  @Override public void flush() throws IOException {
    checkNotClosed();
    if (target instanceof Flushable) {
      ((Flushable) target).flush();
    }
  }

  @Override public void close() throws IOException {
    this.closed = true;
    if (target instanceof Closeable) {
      ((Closeable) target).close();
    }
  }

  /*
   * Override a few functions for performance reasons to avoid creating
   * unnecessary strings.
   */

  @Override public void write(int c) throws IOException {
    checkNotClosed();
    target.append((char) c);
  }

  @Override public void write(String str) throws IOException {
    checkNotClosed();
    target.append(str);
  }

  @Override public void write(String str, int off, int len) throws IOException {
    checkNotClosed();
    // tricky: append takes start, end pair...
    target.append(str, off, off + len);
  }

  @Override public Writer append(char c) throws IOException {
    checkNotClosed();
    target.append(c);
    return this;
  }

  @Override public Writer append(CharSequence charSeq) throws IOException {
    checkNotClosed();
    target.append(charSeq);
    return this;
  }

  @Override public Writer append(CharSequence charSeq, int start, int end)
      throws IOException {
    checkNotClosed();
    target.append(charSeq, start, end);
    return this;
  }

  private void checkNotClosed() throws IOException {
    if (closed) {
      throw new IOException("Cannot write to a closed writer.");
    }
  }
}
